How to avoid Null Pointer Exception in Two Activities Communication

Question

I'm trying to call a method that is inside another class that will populate TextViews when an item is clicked inside AutoCompleteTextView that is also inside an AlertDialogInput.

But my app crashes when I click an Item.

I'm new in android development so any help would be pretty much appreciated.

Custom Alert Dialog Alert Dialog Class

public static class ToPrintAccountSearchDialog extends AppCompatDialogFragment
    {
        private AutoCompleteTextView toprint_auto_account_search_dialog;

        @Override
        public Dialog onCreateDialog(Bundle savedInstanceState)
        {
            AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());

            LayoutInflater layoutInflater = getActivity().getLayoutInflater();
            View view = layoutInflater.inflate(R.layout.for_printing_account_search_dialog_layout, null);
            builder.setView(view);
            builder.setTitle("Search Account");

            List<ForBillPrintConsumerEntities> forBillPrintConsumerEntities = new ArrayList<>();
            toprint_auto_account_search_dialog = view.findViewById(R.id.Alert_Dialog_Account_Auto_Search);
            ForPrintingConsumerAccountSearchAdapter forPrintingConsumerAccountSearchAdapter = new ForPrintingConsumerAccountSearchAdapter(getActivity(), forBillPrintConsumerEntities);
            toprint_auto_account_search_dialog.setThreshold(1);
            toprint_auto_account_search_dialog.setAdapter(forPrintingConsumerAccountSearchAdapter);
                toprint_auto_account_search_dialog.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) 
                {
                    PrintBill printBill = new PrintBill();
                    printBill.getotherinformationbyaccountforprinting();
                }
            });

            return builder.create();
        }
    }

This is the code to show AlertDialogInput Main Activity


Account_No = findViewById(R.id.toprint_Account_No_Value);
        Account_No.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view)
            {
                forPrintAccountSearchDialog();
            }
        });

public void forPrintAccountSearchDialog()
    {
        ToPrintAccountSearchDialog toPrintAccountSearchDialog = new ToPrintAccountSearchDialog();
        toPrintAccountSearchDialog.show(getSupportFragmentManager(), "ToPrintAccountSearchDialog");
    }

this is the method that I want to call when an Item is clicked inside AlertDialog AutocompleteTextview that is also inside Main Activity to populate my textview insid main activity

public void getotherinformationbyaccountforprinting()
    {
        ConsumerAccountForPrinting = toprint_auto_account_search_dialog.getText().toString();
        db = new DatabaseHelper(getApplicationContext());
        sqLiteDatabase = db.getReadableDatabase();
        Cursor cursor = db.ForPrintingGetOtherInfoByAccount(ConsumerAccountForPrinting, sqLiteDatabase);
        if (cursor.moveToFirst()) {
            do {
                String ACCOUNT_NUMBER = cursor.getString(0);
                String NAME = cursor.getString(1);
                String ADDRESS = cursor.getString(2);
                Account_No.setText(ACCOUNT_NUMBER);
                Name.setText(NAME);
                Address.setText(ADDRESS);
                }
            while (cursor.moveToNext());
        }
    }

Data Base Helper

public Cursor ForPrintingGetOtherInfoByAccount(String keyword, SQLiteDatabase sqLiteDatabase)
    {
        String [] projections = {ForPrintingConsumerOtherInfoAdapterByAccount.getOtherInfoForPrintingByAccount.ACCOUNT_NO,
                ForPrintingConsumerOtherInfoAdapterByAccount.getOtherInfoForPrintingByAccount.NAME,
                ForPrintingConsumerOtherInfoAdapterByAccount.getOtherInfoForPrintingByAccount.ADDRESS,
                String selection = ConsumerListOtherInfoAdapterByAccount.getOtherInfoForListByAccount.CONSUMER_ACCOUNT_NO+" LIKE ?";
        String [] selection_args = {keyword};
        Cursor cursor = sqLiteDatabase.query(ForPrintingConsumerOtherInfoAdapterByAccount.getOtherInfoForPrintingByAccount.TABLE_NAME,projections,selection,selection_args,null,null,null);
        return cursor;
    }

projection that calls inside database helper

public class ForPrintingConsumerOtherInfoAdapterByAccount
{
    public static abstract class getOtherInfoForPrintingByAccount
    {
        public static final String TABLE_NAME = "toPrintBill";
        public static final String ACCOUNT_NO = "account_no";
        public static final String NAME = "name";
        public static final String ADDRESS = "address";
    }
}

When I Click The Text View Alert Dialog Pops Up

When I Type number The autocompletetextview will suggest data that has the same value from sqlite database table

But when I click an Item this Happens


java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.AutoCompleteTextView.getText()' on a null object reference
        at com.vicjames.qiimeterreader.PrintBill.getotherinformationbyaccountforprinting(PrintBill.java:224)
        at com.vicjames.qiimeterreader.PrintBill$ToPrintAccountSearchDialog$1.onItemClick(PrintBill.java:189)
        at android.widget.AutoCompleteTextView.performCompletion(AutoCompleteTextView.java:1017)

How can I create communication between my alert dialog class and main activity so i can use that method?

Please have a look at [this answer](https://stackoverflow.com/a/37122385/7948109). In this answer they have used Fragment. you can Implement similar implication using `interface` in `Dialogs` — Rahul Gaur, Jan 27 '20 at 04:04

score 1 · Accepted Answer · answered Jan 28 '20 at 09:20

Use LocalBroadcastManager. Register a receiver in onResume method in your activity, with a specific action, for example "executeMainActivityCode" can be it. For that, you need something like this:

onResume:

LocalBroadcastManager.getInstance(this).registerReceiver(myReceiver, new IntentFilter("executeMainActivityCode"));

onPause (don't forget about this):

LocalBroadcastManager.getInstance(this).unregisterReceiver(myReceiver));

From your dialog, call this code:

LocalBroadcastManager.getInstance(getContext()).sendBroadcast(new Intent("executeMainActivityCode"));

Inside the receiver, call your method in onReceive and you're good to go.

One more problem sir, ```ConsumerAccountForPrinting = toprint_auto_account_search_dialog.getText().toString();``` Since toprint_auto_account_search_dialog AutoCompleteTextview is inside Alert Dialog and Not in MainActivity I'm getting a null pointer exception. How can I solve this — , Jan 30 '20 at 00:13

score 0 · Answer 2 · answered Jan 27 '20 at 09:32

0

You're calling findViewById too early:

Account_No = findViewById(R.id.toprint_Account_No_Value);

This calls it when the Activity is being constructed. Try replacing Account_No in getotherinformationbyaccountforprinting with findViewById(R.id.toprint_Account_No_Value), or setting up Account_No in onCreate after calling setContentView.

answered Jan 27 '20 at 09:32

Ryan M

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That is not the problem, the problem is when I try to execute ```getotherinformationbyaccountforprinting()``` I get a null object exception – Jan 28 '20 at 05:27
Right, I got that part - did you try my suggestion? You're calling `findViewById` too early, it sets `Account_No` to `null`, so it's `null` when you access `Account_No` in `getotherinformationbyaccountforprinting`. If you call it in `getotherinformationbyaccountforprinting` like I suggested, it shouldn't be `null` at that point. – Ryan M Jan 28 '20 at 20:24

score 0 · Answer 3 · edited Jun 20 '20 at 09:12

As I suggested in the comment you can use interface to communicate between Activities/Fragments/Adapters/etc`.

1. create an Interface

public interface DataTransfer{
    void sendData(String data); //change parameter to whatever you want
}

2. implement the interface in your activity

3. pass interface in alertDialog

ToPrintAccountSearchDialog toPrintAccountSearchDialog = 
    new ToPrintAccountSearchDialog(this);  
    // here this will pass the implemented interface

4. in your dialog receive the interface using constructor


private DataTransfer dataTransfer;

public ToPrintAccountSearchDialog(DataTransfer dataTransfer){
    this.dataTransfer = dataTransfer;
}

5. User this dataTransfer to pass data to activity

dataTransfer.sendData("Some important data");

6. In your activity there will be an `@Override` method `void sendData(String data);`

@Override
public void sendData(String data) {
    Log.e("TAG", "sendData: this data is from Dialog " + data);
}

Edit 1: explanation

There is 1 Activity A and 1 DialogFragment B

B wants to send data to A

A gives B an interface so when B calls dataTransfer.sendData("Hello");

A will also call it's own overridden sendData(String data);

Now if you print this

@Override
public void sendData(String data) {
    Log.e("TAG", "sendData: " + data);
}

This will print

Hello

You can call any other method from sendData

Hope this will help!

Please ask if you need more help

How is this going to execute the method ```getotherinformationbyaccountforprinting()``` ? that will populate textviews inside the main activity — , Jan 28 '20 at 00:43
add this method inside `sendData` and pass the data as parameters — Rahul Gaur, Jan 28 '20 at 03:43
Can u please elaborate your answer more? Sorry I'm new to this:( — , Jan 28 '20 at 05:28
Please check my updated answer, please ask if you need explanation related to anything else — Rahul Gaur, Jan 28 '20 at 08:58

score 0 · Answer 4 · answered Feb 02 '20 at 23:33

Found an answer on how to get the text from AutoCompletetextview from another class or a fragment

Inside Main Activity on Create Add fragment support

        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        ToPrintAccountSearchDialog toPrintAccountSearchDialog = new 
        ToPrintAccountSearchDialog();
        ToPrintNameSearchDialog toPrintNameSearchDialog = new ToPrintNameSearchDialog();
        fragmentTransaction.add(R.id.activity_print_bill,toPrintAccountSearchDialog);
        fragmentTransaction.commit();

Then Inside your fragment onCreate Add the following codes

            toprint_auto_account_search_dialog = 
            view.findViewById(R.id.Alert_Dialog_Account_Auto_Search);
            toprint_auto_account_search_dialog.setOnItemClickListener(new 
            AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l)
            {
                String account_no_to_print = 
                toprint_auto_account_search_dialog.getText().toString();
                PrintBill printBill = (PrintBill) getActivity();
                printBill.account_no_to_print(account_no_to_print);
                dismiss();
            }

Then Inside Main Activity Create a variable and put the value of autocompletetextview like this

    public void account_no_to_print(String account_no)
    {
        this.ConsumerAccountForPrinting = account_no;
    }